Heating coil



P. ARANT HEATING COIL Oct. 9, 1951 E r1 lllll'l A mlnl E INVENTOR BY M*ATTORNEYS OCt. 9, P, ARAN-r.

HEATING COIL Filed'Aug.' e, 1946 5 sheets-sheet 2 v @da i" v i INVENTORfel'lyl'mzi BY @man ATTORNEYS oct. 9, 1951 P. ARANT i 2,570,630

HEATING COIL Filed Aug.A 6, 1946 5 Sheets-Sheetl 5 oct.' 9,v 1951 P.ARANT` 42,570,630

HEATING COIL A Sheets-Sheet 4 Filed Aug. 6, 1946 lNvENToR ATTORNEYSatented ct. 9, i951 HEATING COIL Perry Arant, Alhambra, Calif.,assi'gnor to Clayi ton Manufacturing Company, Alhambra, Calif., acorporation of California Application August 6, 1946, Serial No. 688,720

The present invention relates to a heating coil construction,particularly adapted for use 1n *steam generating apparatus, and to themethod f making such coil.

More specifically, the invention relates to a heating coil constructionincluding a preheater section, a water wall section and a generatingsection, arranged in series in the order mentioned, and to the method ofmaking such coil.

One of the principal objects of the invention is to obtain compactnessand reduction in size of the heating coil for developing a given ratedhorsepower without sacrificing eiciency and economy.

Another object of the invention is to provide a heating coilconstruction which has-great stability by virtue of the fact that itenables the uid to be kept in a substantially liquid state until it isdicharged into aV steam generator or other zone of low pressure.

Another object of the invention is to provide a heating coilconstruction which will have a greatly increased life.

Another object of the invention is to provide a heating coil including aWater wall arranged so that fluid can be returned from the water wallsection to the main portion of the heating coil without the use of anyexternal risers.

Another object of the invention is to provide a heating coilconstruction wherein liquid will always be present in the portion of thecoil nearest the rebox to thereby assure that the radiant heat of therebox will not evaporate the water therefrom so as to cause such portionofthe coil to be empty when the burner is re-started.

Another object of the invention is to provide a combustion chamberlining means for steam generating apparatus which will eliminate theusual great thickness of insulating material normally required tosatisfactorily resist the great heat generated by the combustion of fuelwithin the combustion chamber.

A further object of the invention is to provide a heating coil having awater wall section serving as a portion of the combustion chamber liningarranged so as to eliminate condensation of fuell 7 Claims. (Cl. LZ2-250) substantially constant rate so that a forced draft is maintainedthrough the heating coil for the products of combustion, with suicientexcess air supplied under pressure for diversion and use to maintain lowjacket temperatures.

Other objects and features of the invention will be apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

Fig. l is a longitudinal sectional view through a steam generatingapparatus embodying the present novel heating coil, combustion chamberlining, and jacket cooling construction;

Fig. 2 is a sectional View taken on the line 2 2 of Fig. 1;

Fig. 3 is a sectional View on the line 3 3 of Fig. 1 and particularlyillustrating the construction of the base of the apparatus and the airdeflecting means for maintaining a low jacket temperature; Y

Fig. 4 is an enlarged fragmentary sectional view taken on the line 4 4of Fig. 3, and illustrating the manner in which the shell surroundingthe heating coil is assembled with the base and one of the legs of theapparatus;

Fig. 5 is an enlarged fragmentary sectional View taken on the line 5 5of Fig. 3, and illustrating the means employed for supporting thehelical water wall coil perpendicular with respect to the base of theapparatus;

Fig. 6 is an enlarged fragmentary sectional view l taken on the line 5 6of Fig. 3, and illustrating one of the apertures which establishcommunicaticnbetween the annular air space in the base and the annularair space in the jacket, for facilitating scooping of the moving airfrom the base into the jacket air space;

Fig. 7 is a somewhat diagrammatic perspective view illustratingapparatus suitable for making the double wound water wall section of theheating coil;

Fig. 8 is an enlarged sectional View taken on the line 8 8 of Fig.r 7,through the clamping means for securing the ends of two pipe sections tothe mandrel of the winding apparatus;

Fig. 9 is a diagrammatic plan view showing the relationship of themandrel clamp and pipes at the starting of the winding operation;

Fig. 10 is a view similar to Fig. 9 showing a portion of the double coilwound upon the mandrel with the turns closely adjacent each other,

'and spacer elements positioned to effect winding of the remainder ofthe coil with the turns spaced a predetermined distance apart;

Fig. 11 is a sectional view taken on the line Il 'l I of Fig. 10;

Fig. 12 is a diagrammatic view illustrating the double wound coil in asubstantially completely wound condition and with a shell slipped overthe wound portion thereof;

Fig. 13 is a diagrammatic view illustrating the ends of the double woundcoil interconnected by a return bend and with the shell completelyenclosing the coil;

Fig. 14 is a diagrammatic view illustrating the manner in which two pipesections pre-connected by a U-bend may be clamped to a mandrel to effectwinding thereof;

Fig. 15 is an enlarged fragmentary sectional View on the line I-I5 ofFig., 14 illustrating the clamping means for securing the U-bend to themandrel; and

Fig. 16 illustrates a length'y of; pipe pro-vided1 with a U-bendintermediate its ends and adapted to be wound upon the mandrel of Fig.14.

Referring now to Figs.l l to 6, inclusive, of the drawings, the numeral.I generally identifies the steam generating apparatus which includeslegs 2` supporting a housing comprising a base 3, an intermediate jacketsection 4, and a top section 5.

The base 3 includesV a lower horizontal, circular bottom wall 5 having aperipheral flange 1 welded to the lower end of an outer ring 3. The base3 further includes an upper horizontal, circular wall 9 provided with aflange I9 at its outer periphery welded to the lower end of anintermediate ring I I arranged concentric with the ring 8. lIhe walls 6and 9 are spaced apart to provide an air space i2 therebetween. Aplurality of air deflecting baffles I3 are spot welded to the undersideof the Wall 9 and serve as spacing means between the walls 9 and 6. Anair supply duct I4 is disposed below the wall 6 and secured thereto inany desired manner. A blower I5 forces air under pressure into the ductI4; The wall 5 is provided with a central air inlet opening I5communicating with the air supply duct I4. The duct I4 is preferablydesigned to deliver air to the opening I6 moving at high velocity in acounterclockwise, spiral or volute path and may be constructed, forexample, in the manner disclosed in Kerrick Patent 2,284,906. The wall 9is provided with an opening I1 arranged concentric with the opening I5of the wall 5, but of smaller diameter, and has a bushing I8 mountedtherein. The bushing Idhas a passageway I 9 which establishescommunication between the .air supply duct I4 and a combustion chamber2i] within the jacket 4 above the base 3. The passage in the bushing i8is smallerthan the opening I6 and therefore a portion of the airsupplied through the duct I4 is deflected laterally or outwardly by thewall 9 into the space I2 between the walls 5 and 9 to maintain a lowjacket temperature, as will be explained later.

It will be understood, of course, that aforced draft is maintained inthe steam generating apparatus I and to this end air is forced into thesupply duct I4 by the blower I5 which is capable of supplying a greatervolume of air than is required for complete combustion of the fuel, withsufficient excess for diversion into the air space I2 for jacketcooling.

An inner ring 22 is preferably-welded at its lower end to the upper sideof the wall 9 and is arranged concentric with the rings 8 and Il. Thering 22 is considerably smaller than the ring II providing a space 23between the outer periphery thereof and the inner periphery of the ringII. Suitable refractory material 24 is disposed between the bushing I8and the ring 2,2 and is supported by the wall 9. The upper sur- 4 face25 of the refractory material 24 is inclined downwardly toward thebushing I8, as best shown in Fig. 1.

The air inlet duct I4 supports a burner device 25 including a pair ofnozzles 21 for atomizing the fuel introduced into the combustion chamber20. A pipe 28 is connected to the burner 25 for supplying fuel thereto,and electrode means 29 is arranged to initiate ignition of the fuel.

The steam generating apparatus I includes a novel heating coilconstruction generally identied by the numeral 35. The heating coil 35includes a preheater section 35, a water wall section 31 and agenerating section 38, arranged in series flow, but with the generatingsection 38 disposed below the preheater section 36 and within the upperend portion of the water wall section 31. The preheater section 35 hasan inlet 39 and may include any suitable number of spirally woundpancake coil sections 4E! arranged in superposed relation. In oneoperative form of the invention, the preheater section 36 includes, forexample, eight individually wound pancake coils 4D, as illustrated inFig. l, and the inner end or outlet 4I of the uppermost pancake coil 40is welded to the inner end or inlet 42 of the second pancake coil 40,and the outlet 43 of said second pancake coil is welded to the inlet 44of the third pancake coil 4U, and so on, throughout the height of thepreheater section 36, with the result that the pancake coils 4i) vareinterconnected in series and the outlet of the preheater section 36 islocated at the outer end 45 of the lowermost pancake coil 45.v

The Water Wall section 3,1 consists of a double wound helical coilpreferably made of two predetermined lengths of pipe 50 and 5Iinterconnected at one end in the finished coil by a return bend 52. Themethod of winding the double coil 31 is set out in full hereinafter. Theend 53 of theY pipe 5D, remote from the return bend 52, is welded to theoutlet end 45 of the preheater section 35, and the corresponding end 54of the pipe 5I. is welded to the inlet -55 of the generating section 38.The double winding of the water wall section 31 provides a constructionin which the fluid flows downwardly for the full length of the pipe 5 9,or in a direction counter to that of the path of travel of thecombustion gases, and then reverses flow at the return bend 52 and flowsupwardly in the. pipe 5I toward its end 54 in the same general directionas the travel of the combustion gases; the result being that the fluidflow in any two adjacent turns of the water wall section 31 occurs inopposite directions, as indicated by the arrows in Fig. l. in thepresent construction, thewater wall 31 is illustrated as having, for`example, about sixteen complete turns disposed vertically one above theother, with the upper half, or rst eight turns, in substantiallyabutting relation and with the remaining eight turns spaced about 1A;inch apart, and maintained insuch spaced relation by clips 56 welded toor inserted between adjacent turns. The object of the different spacingof the turns of the water walllsection 31 will be explained later.

The generating section 38 is shown in Fig. 1 as consisting, forexampleof five individual pancake coils 30 arranged so that the innerend 5I of the uppermost or first pancake coil 60 is welded directly tothe inner end 52 of the lowermost or fifth pancake coil 6U. The outerend 53 of the lowermost pancake coil 60 is welded to the outer end 64 ofthe next adjacent, or fourth, pancake coilBU, the inner end of theVfourth pancake c oiLis weldedto the inner end G ljofthel third pancakecoil, theouter end 61 of the thirdpancake coil is welded to the outerend68 of the secondpancake coil, andthe inner end 89 ofthe secondvpancake coil is welded to one end 1 0 of a discharge pipe 1|. Y

Thus, the fluid discharged from the upper end 540i thewater wall section31 enters the iirstV pancake coil 60 of the generating section 38 andflows therefrom to the lowermost pancake coil andthen upwardly throughthe fourth, third andY second pancake coils and into the dischargepipe,1| by owing inthe samegeneral direction as tlie travel of thecombustion gases. l n c,

The pancake ncoilslli are slightly spaced apart and are heldin suchspaced relation by clips 12 welded or otherwisesecured to the Houtermostcoils thereof. AV baiiie plate 13 is arranged in the generatingsectionlbetween the second and third pancake coilsY 60, the fourth andfifth pancake coils 60 and belowV the fifth pancake coil 60 to preventthe direct passage of combustion gases through the corer14 formed at thecentral portion of the generating section 38. Soot blowers (not Shown)are preferably disposed between the pancake coils 40 of the preheatersection 36.

vIt will be convenient, at this point, to describe the' apparatus andmethod employed in making the double wound water wall section 31, andreference will Vtherefore be made to Figs. '7 to 13, inclusive.

' In Fig..'7, the numeral 80y generally identifies the coil lwindingapparatus, and such apparatus includes a table 8| having a top 82 andlegs 83 which are adustable vetrically to va1y the inclination'and/orheight of the table top 82 relative to the coil windingrapparatus 80.The table top 82 serves as a 'support for the pipes 50 and 5| previouslyreferredto. The winding apparatus '80 further includes a base' 84 havinga pedestal l85 mounted at one end thereof, and aconventionallgear"reductionunit 85 mounted upon said pedestal. A shaft81 driven by areversible motor 81?'cons'titutes a drive for the gearreduction unit'85, and a'shaftA 88 constitutes the driven shaft 'of thegear reduction unit 85. The shaft 88 drives a. shaft |38a having ahollow cylindrical mandrel 89 mounted thereon provided with a angev90 atthe inner end thereof. Theouter end of the shaft 80a carries a bushing9| (Fig. '7), which is Vsupported in a journal 92 comprising hingedsections Y93 and 94 which are releasably held engaged with the bushing9| by the coaction of a ,bolt 95 pivotally mounted upon ears 96 on thebearing section 93 and projecting between ears 91 on the bearing section94, the latter be- Yingengaged by a thumb screw 98 threaded onto thebolt 95. The journal 92 is carried by a triangular frame 99, which isdetachably supported upon the base 84 upon studs |00 projectinglongitudinallyrfrom one end |0| of said base. The frame 99 isremovablyretained in position upon the studs |00 by pins |02. y Themandrel 89 carries a clamp |05 for securing the ends 53 and 54 of thepipes 50 and 5| to the mandrel 89 to effect winding thereof. The clamp'|05 includes a plate |06 having a stud |01 (Fig. 8) projecting inwardlytherefrom and normallyV disposed in the stem portion of a T-shaped slotI 08 formed inthe mandrel 89 at a point near the unanged end thereof. Awasher |09 is disposed upon the stud |01 for engagement with the innersurface o f the mandrel 89 and a wing nut 0 is threaded onto the stud|01 Afor detachably sec-fing the degli.) '.05 t0. the mandrel 139-1 The,

plate |06 carries circumferentially projecting ngers and'll2 ofadiameter small enough to be snugly received in the ends 53 and 54 of thepipes 50 and 5|, respectively. The opening |08 is suiciently large toenable the plate |06 and the fingers and ||2 carried thereby to passtherethrough for removal from the interior of the mandrel 89, as will beexplained later.

Fig. 9 illustrates the coil winding apparatus 80 in the position itassumes at the beginning of a winding operation. Thus, it will be notedthat the mandrel 89 has been rotated to a position where the clamp 05 isdisposed at the lower side thereof, and the pipes 50 and 5| have beenadvanced by the machine operatoruntil the ends 53 and 54 thereof havethe ends of the ngers ||2 and III, respectively, received therein. Thisprovides a quick and simple way of securing the ends 53 and 54 of thepipes 50 and 5| to the mandrel 89 to effect winding thereof. The motor81a is' started to cause driving of the mandrel 89 in aclockwisedirection, as viewed in Fig. 7, whereupon winding of the pipes 50 and 5|upon the mandrel 89 commences. The pipes 50 and 5| are guided during thewinding operation by the operator to effect close winding of, say, thefirst eight turns of the coil. The motor 81a is then preferably stoppedand a spacer element or plate I I4 (Fig. 10) is inserted between thepipe 50 and the last wound turn of the coil, and another spacer elementor plate ||5 is inserted between the pipes 50 and 5|. The spacerelements ||4 and ||5 are supported upon the table top 82 and extend to apoint well under the mandrel 89 as will be apparent from Fig. 11. Thethickness of the plates I|4 and I5 will vary in accordance with thedesired spacing of the turns of the lower end portion of the water wallsection 31, and in the illustrative example shown, these plates are /zinch thick. The motor 81a is restarted to drive the mandrel 89 in thesame direction as before to continue the winding of the coil. Thewinding of the coil is interrupted as the ends 53a and 54a (Fig. 12) ofthe pipes 50 and 5| approach the edge of the table top 82 nearest to themandrel`89. The clips 56 are now preferably attached to or insertedbetween the spaced turns of the coils to maintain the same spaced apart.

The thumb screw 98 may be loosened to release the journal 92 from thebushing 9| and the pins |02 removed to permit detachment of the frame 99from the base 84. A shell I|6 of predetermined internal diameter maythen be slipped over the unsupported end of the mandrel 89 onto thewound portion of the double coil until it engages the unwound ends ofythe pipes 50 and 5I, as illustrated in Fig. 12. The driving torque onthe mandrel 89 is then released by reversing the motor 81a and the twohelical coils formed from the pipes 50 and 5| are allowed topartiallyunwind into engagement with the inner surface of the shell IIB. Ihe pipeends 53a and 5,4a are evened up, if necessary, and the return bend 52 isthen welded thereto. The ends 53a'and 54"l with the return bend 52attached thereto are then bent around the mandrel 89, and the shell IIBis then pushed over the remainder of the coil into engagement with theflange 90, as shown in Fig. 13. The wing nut |I0 is then loosened,thereby releasing the clamp |05 and said clamp is then moved toward thehead of the T-slot |08 so that it can be withdrawn through said slot to,Vparrait the double wound coil Bland the, shell 7 |6 to be removedsimultaneously from the man drel 89. Y The shell |6 is formed from arolled sheet of metal and its Vlongitudinal edges are placed linabutment and. a strip IIB (Fig. 12) is welded to the shell llt at theabutting portions thereof to hold the same in cylindrical form. Aplurality of anglebrackets H9 is welded to the shell H6 adjacent one endthereof.

The lowerrnost turn of the coil 31, cf course, is arranged on -a helixand in order to 'support the same vertically, a plurality of strips orfeet V||1 (Figs. 3 and 5) of different vertical height are welded tothelo'wer side of said turn.

After the feet I |1 have been welded to the water Wall-section 31, theshell VHt is slipped down and the end 54 of said section is welded tothe inlet end 55 of the Ygenerating section 33, and 'the end 53-iswelded YtoV the outlet end 45 fof the preheater section 36. The shell li6 is restored/to its original position but is of insuiiicient length toenclose the preheater section 3E and, hence, a second shell |2e V(Fig.1), having the main inlet 39 and the discharge pipe 1| extendingtherethrough, i-s arranged in telescoping rel-ation with the shellll andis Awelded at its lower end `|-2| to the 'upper end of the vshell H6.

A crossbar i272 (Fig. 12.) extends across the upper portion of the shell|29 and the opposite ends thereof are secured 'to said shell by brackets|23 bolted to said cross'bar and shell, respectively. A second bar |24arranged at right angles to the crossbar |22 has one end welded to theadjacent side of the crossbar l 22 and its other end Yfastened to theshell i2@ by a bracket |25bolted to both said bar and shell. Another bar|21 has one end thereof welded to the opposite side of the crcssbar |22and its opposite end is secured by a bracket |23 and suitable bolts tothe 'shell l i6. A tie bar |29(Fig. l) bridges the crossbar |22 and`over-lies the adjacent end portions of the bars |24 and |121 and iiswelded along its lower edges to all of said bars 'to stiften the sameand form aV rigid bridge across the crossbar |22. A hook member |3543has a shank |3| disposed at the point of juncture-of the bars |22 andE21 and is welded thereto and to the tie bar i297. rThe lower edges ofthe bars |22, |-2ii and |21 lare preferably welded to the upper pancakecoil section Il@ of thepreheater section V36. venient device forhandling the entire shell and coil assembly by means ef a crane (notshown). After the assembly of the coil and shell has been completed, asabove described, the same is subjected to a conventional heat treatmentto relieve l all stresses. and strains therein.

After the coil assembly has been heat treated, a stainless steelcylindrical sheet liner |32 (Fig. 1)4 is inserted within the lowerportion of the water wall section 31. The height of the liner |32 ispreferably such that it extends upwardly into the region of thegenerating coil section 38. The upper end of the liner |32 is curvedinwardly, as indicated at |33, to facilitate such insertion. The liner|32 is preferably made of stainless steel, that is, a chrome-nickelsteel, commercially known as 18-8 stainless steel, although otherstainless steels of different ratio 'of chrme to nickel have been foundto be satisfactory. Ordinary sheet iron may also be used in making theliner |32, but the life of such a liner is relatively short andstainless steel is preferred because i eliminates the replacementproblem. 'i The thickness of the stainless steel liner-|3`2 is ofv theorder of v'04 inch to -.14 incl-'i and-prefee' The hook |33 thusprovides a cone ably .'06 inch. The heavier :gauge materialrs capable ofslightly deforning Vout of round individual turns of the/water wallsection 31 so that good heat transfer -contact can be maintained betweenthe outer surface of the liner |32 and the inner surface of all of thecoil turns. The liner |32 is made by rolling a flat sheet of stainlesssteel into cylindrical form and then welding or otherwise securing thevertical edges together. Afterward, one 'end is rolled to turn the sameinwardly to provide the rounded edge |33, pre@- viously referred to. Y,

The external diameter of the liner |32 is dependent upon the internaldiameter of the water wall section 31 andtheir relative rates of thermalexpansion. -In this connection, the liner; |32'isv made of -suchexternal diameter'that it canbe readily slipped into the water wallsection V31 with some'slight clearance, the clearance being vsuch thatit vwill subsequently be eliminated under normal combustion temperaturesby expansion of the liner |32 into positive contact with the innermostsurfaces of the water wall section 31.

In one operative example of a horsepower unit, the internal diameter ofthe turns of the water wall section 31 was 231A; inches andthe cuterdiameter of the liner- V|32 was 22% inches, thus allowing 1/4 of an inchtotal clearance for expansion. The internal diameter of the turns of thewater wall section 31 is held to a desired dimension by the expedient ofemploying the shell H6 of' predetermined internal diameter and the stepof allowing the helical coils formed from the pipes '50 andV 5| to onlypartially unwind after the shell llt` has been slipped thereover, asde-7 scribed herein in connection with the method of making said waterwall section;

No special heat treatment is given to the stainless' steel liner |32; itis simply `inserted within the water wall-section 31 after the `coil`assembly 35 has been stress-relieved. In operation, the liner '|32 willexpand into positive yengagement withv the surrounding turns of thewater wall section 31, and in some instances may bulge slightlyoutwardly betweenadjacent turns, as illustrated to an exaggerated degreein Fig. 4. Normally, however, the liner |32 will contract upon cooling,so that it can be readily removed from the coil 31. After the unit hasbeen in operationfor a period of time, the coil 31 and the liner |32take a more or less permanentset, in contact, as 'a result of the -lossof elasticity due to repeated heating 'and cooling. v

When the pipe being wound to form the water wall section 31 is smallerthan one inch in external diameter, it is unnecessary torplace the shell||6 Ythereover to limit the. extent Vof. un` winding thereof. Thereasonfor this is that, with a smaller diameter pipe, the pipe takes amore or less permanent set as it is wound upon the mandrel 89,'and doesnot tend to unwind to any substantial degree, thus no vdiinculty arisesin maintaining a nxed internal diameter. However, when pipe, such asthe-pipes 50 and 5|, of an external diameter greater than one inch isWound upon the mandrel 89, the inherent elasticity of the pipe would,'unless constrained, cause the same to unwind to a considerable degreeand result in coils'of varying'internal diameter. I To avoid this, theshell H6, of predetermined internal diameter, is* slipped over the Vcoilon the mandrel 89 to limit the extent of unwinding cf the helical coils'when the driving torque 'on said mandrel isreleas'ed. In thisr'manner,it is possible to maintain the' internal diameter m'of the double woundcoil 31 to a givenz'size so' that ai liner |32 of predetermined externaldiameter will properly vlit and expand into positive engagement with theinner surface of the coil during operation of the steam generatingapparatus I.

v`While the aforedescribed method of winding the water wall section 31contemplates joining the ends of the pipes 50 and 5| by a return bend52, after said pipes have been wound upon the mandrel 89, Figs. 14 and15 indicate the manner in which a double wound coil can be formed byfirst interconnecting the ends of two pipes by a return bend andclamping the returnbend to the winding mandrel. Thus, two lengths ofpipe 50b and may be rst interconnected by a return bend '52 length oftubing may be bent substantially medially of its length'to provide areturn bend 52c and substantially parallel portions 50c and 5|, asdiagrammatically illustrated in Fig. 16. In either event, the tubularmaterial to be wound is connected to a mandrel 89h, ofv a windingapparatus 80h similar to the apparatus 80; by a clamping devicegenerally identiedby the numeral |05". The clamping device, |0511'includes a bracket |06b which is riveted' or otherwise permanentlysecured to the inner face ofthe mandrel 89b adjacent an opening |08".Clamping fingers |||b and ||2b extend through the opening |08b and gripthe inner and'outer portions of the U-bend 52h, as best illustrated inFig. l5. A wing bolt ||0b extends through the clamping lingers 7|||b and||2b and is bracket |061.

After the U-bend 52D has been clamped tothe mandrel 89h, one turn'of thepipes 50| and 5|b is wound upon the mandrel 09h, and spacing elements,such as the elements 4 and ||5 shown in Fig. 10, are disposed betweenthe pipes 50h and '5|b and between the pipe 50h and the adjacent woundturn of the coil, as will be readily understood, to eiect spacing of theturns adjacent the return bend 52b a predetermined distance apart. Afterthe desired number of spaced turns'has been wound uponthe mandrel 89h,the spacing elements are removed and the remainder of the pipes 50b and5|b is wound upon said mandrel with the turns in contact, under theguidanceof the operator.

It .will also be understood that when pipe in excess of 1" externaldiameter is wound upon the mandrel 89h, winding of the coil will becontinued until the pipes 50|u and 5|b have been almost completely woundthereon Then a shell, similar to the shell H6, will be slipped over thewound portion of the coil. and the winding torque released slightly topermit the turns to partially unwind and expand into engagement with theinner surface of the shell. Of course, the shell will be slipped overthe mandrel 891D in a manner opposite to that shown in Fig. 12, i. e.,so that the brackets ||9 mounted upon the shell will be disposedadjacent the end of the coil having the return bend 52h. The unwoundportions of the pipes 50h' and 5|b are'then bent against the mandrel 89band the shell is slipped farther onto the mandrel to completely enclosethe coil.

The removal of the wound coil from the mandrel 80h, irrespective ofwhether it is enclosed in As an alternative to this procedure, a singlethreaded into the a shell or not, can be effected by removing theContinuing now with the description'of the remainder of the' steamgenerating unit I, four inverted U-shaped members |35 (Figs. 3 and 4)are disposed in the space 23 and their end edges are respectively weldedto the rings ll'and `22L The U-shaped members |35 are arranged to serveas supports for the feet ||1 at the lower end of the water wall section31. The members |35 are also vertically aligned with the brackets H9secured to the lower end ofthe shell ||6. Bolts |36 project through thebracketsr |19', the horizontal wall of the U-shaped members |35, throughopenings in the bottom walls 9 and" 6 and through an opening in thesupporting legs 2, as best illustrated-in Fig. 4, for securingthe shell6 in assembled relation with the base 3 and legs 2. The legs 2 areadditionally secured to the base 3 by bolts |38 which extend through thering 8 and into a reinforcing stripV |39 (Fig. 4)- engaging the innersurface of the ring 8.

Layers |40 and |4| of heat insulating material surround the shells I6and- |20 to` minimize heat losses. A cap member |42 is disposed abovethe upper end of the shell |20 and: is vsecured thereto in any suitablemanner. The cap |42 has a central flue opening |43 and a sleeve |44provided with openings |45 Vsurrounds the ilue opening |43. A layer ofinsulating material |46 is disposed outwardly vof the sleeve v|44 andoverlies the upper surface of the cap |42, as shown.

The outer ring 8 of the base 3 has an outwardly extending flange |41(Figs. 1 and 3) at-its upper end, and the intermediate ring has anoutwardly projecting flange |48 which overlies and engages the flange|41. The lower endof the jacket section4has an outwardly extendingiiange |49 that rests upon Vthe flange. |48. The flanges |41, |48 and|49 may be bolted or welded together, as desired. The jacket 4 hasaliningvof insulating material |50 which is arranged outwardly of theinsulating materialA |4| to provide an annular air space |5| completelysurrounding the insulated heatingV coil assembly. f

The upper end of the jacket 4 has an outwardly extending flange |52(Fig. '1) f and the-cap 5 has a similar ange |53 resting uponltheflange|52. The flanges |52 and |53may be bolted or welded together, asdesired. The sleeve |44 projects into an opening |54 in the cap 5 sothat an air space |55, communicating with-the annular air space V| 5|,is formedY between 4the inner surface of said cap and the insulatingmaterial |46, the openings |45 providing communication between the airspace |55 and the ue openingv The ange |48 of the intermediate ringcontains a plurality o-f circumferentially spaced apertures |56 whichhave their edges bent, as indicated in Fig. 6. to form air scoops facingin a counterclockwise direction. These apertures establish communicationbetween'theannular air space |5| in the jacket 4 andanannular air space`|50-between thef'rings 8 and Accordingly, air travelling in acounterclockwise, spiral path and introduced `through the opening I6into the air space 2 in the base 3 is deflected outwardly by theoverlying portion of the wall 0 and the baflies I3 into the air space|58,` and is sc'ooped by the leading edges ofthe apertures |56; into theannular jacket air space |5| to remove any heat `that has passed throughthe insulating layers |4|-| 42, whereby to maintain theitem perature ofthe jacket 4 at a minimum to prevent undue heating of the lboilerroom orchamber in which` the steamA .generating unit isy installed. The: heatedair forced out oiY the air space |51 passes through the air space l55,open ings |245 and is exhausted into a stack |59 surrounding the opening|54 in the cover 5T.

It will be notedfrom Fig. l that thelower end of the liner |32 restsupon the upper surface 25 of therefractory material 24'. The object ofsuch arrangement is to provide a seal at the lower end of the liner |32that will keep the fuel conned within the combustion chamber 2li so thatit cannot leak into the-space occupied by the water wall section 31 andthe insulating material 14B, |41' and i150. The seal is particularlyimportant when gaseous fuels arel used inasmuch as under such conditionsit would be highly undesirable to-havecombustible-material leak out ofthe combustion chamberinto the air space [5l surrounding the coil 35 inView of the fire hazard which itwould present. In the case of liquidfuels, such as oil, the same might also, constitute a re hazard, butoil'presentsthe further objection in that it would be absorbed by theinsulating material anddecrease the efciency thereof; Y

In actual' operation, operating temperatures in steam generatingurn-itsVK ofthe character comprising the present invention range from250()o FL to 2900F. dependingupon the size of the unit.V The highesttemperaturev which present-day refractory materialsI are capable ofwithstanding is about 2900 to 3000 F. maximum, whichY does not leave anymargin of temperature resistance to resist direct flame impingementcausing heating above the maximum and which most generally` causesrefractory failure at the point oi flame impingement. The presentinvention eliminates the use of refractory' material in the side wallsof the combustion` chamber by incorporating a water wall section 31 anda stainless steel liner 132. which was unexpectedly found tosatisfactori-ly solve the problem ofgresisting excessively biencomhnstion chamberv temperatures. In fact', the present liner haswithstood operating temperatures of 200W F. without failure. Thestainless steel liner |32 serves not only to rapidly transfer'heattherefrom to tbe water wall section 31' to thereby avoid' excessiveover-heating of said linerhut transfers enough heat to the coil 31130prevent condensation of liquid fuels and moisture thereon.

A further advantage.- nf thel sheet metal` liner f3! and water wallarrangement 3T disclosed herein is that` it greatly ontl'astsrefractoryY Walls., but what is more important. makes it possible tomake the unit more compact by not occu'oving anywhere near as great a@nace as would normally be reunir-ed for the thir-.lrness of refractorymaterial necessary tn withstand the same combustion cb ambertemperatures. Y

It is important to make the metal liner i732V of a. dimension that willallow the liner to expand and make positive contact with the turns ofthe water wall 31v upon thermal expansion thereof. Ifinsuilicientclearance for expansion is allowed, the liner {B2-'will' buckle uponexpansion andburn or scale at thebuckled points. On the other hand',iftoo much clearance is provided, the liner will not expand intolheat-transferring contact with the water wall 31 and burn or scalebecause of improper cooling thereof.

Insoiar as the operation of the heatingf coil itselfj i-s concerned, theliquid to beV heated is introduced throughthe inlet 39 into thepreheater section 36 so that the liquidv is preheated 'before itAentersy the water wall section 31. Hence, too low temperatures in thewater wall section 31 are avoided", andi this eliminatescondensation'yof fue-l vapor which: would' cause carbondeposits. It alsoeliminates collection of and condensation of moisture from the air onthe externalsurface of the water wall tubing, which would result inactive corrosion. The water wall' section 31, as previously explained,is double wound so that the uidflows downwardly in the water wallsection in theV helical coil portion formed by the pipe 50 and upwardlyin the Water wall sectiony 3-1 through the helical coil portion formedby the pipe 51|", to. be discharged' into the uppermost pancake coil EEof the generating section 38. The fluid passes through the firstApancake coil'- 60 of the generating section 38 and then directly tothebottom pancake coil 6U, and' at this point changes from counterflow todirect ilow and passes-np- WardlyV through the balanceof the pancakecoils lill and is then discharged' through the riser pipe Il intoafsteam separator (not shoW-n-)- orp any other apparatus. y Y

The upper turns of the water wall, section 31 are'arranged closelyadjacent each otherA for` the purpose of providing a combustiongassealfatfthe criti'calipoint or level ofthe combustion chamber 2G;Whereas; the lowermost turns of thewater wall sectionY 312 are spaced*apartl to facilitate absorption of theY radiant heatof the liner |32,the surface ofthe Water wall coils 31' directly in contact with theliner |32', of course, absorbing heat by direct conduction. TheVvertical spacing or pitch of the lower coilsv of the vs fater wallsection 31' is such that' sucien-t' heat transfer will be eiiected bydirect conductionand radiation to maintain the liner |32 sufficientlycool'to prevent overheating or burning out of the same.r

The Vdouble Wound water wal-I 31" Vprovides a return pass for the uidwithout requiring the necessity of employing any external piping ortubing.. At` the same time, the ow of the fluid through the water wallsection 31v resultsv in the absorption of heat from the combustionchamber and from theY liner i372 so that the fluid is di'schargedrintothe generating section 38- at aslightl-yfelevated temperature abovethat at which it entered' the water wall' section 31. f f

The object of' connecting the upper pancake coil 89 ofthe generatingVsection 38 to the lower pancake coil of said section is to provideaconstruction in which some fluid is always present in the pancakeV coilEl! nearest tothe lconibustioli chamber 2E), but which fi-uidfisnot atthe rmaximum temperature tov which the unit is capa-ble of heating thesame. In other words, additional heat is absorbed in the generatingsection 38 by the fluid as it' travels in a generally upward directionthrough the generating section 38'. The principal' advantage of` such anarrangement is that. excessive temperatures in the lowermost pancakecoil 60 are avoided. The arrangement also creates a higher temperatureYdifferei-itial between 'the temperature of the uidV inthe coil andthetemperature ofthe combustion gases, which increases the effectiveness ofthe. heating coil. In fact, thermal ellicienciesasr high as $270'. arecommonly attained in units embodying the coil assembly 35. A Y

The present coil construction notA only` nia-kes it possible to developa givenboiler horsepower with less heating' surface than previous unitsdesigned toy develop the same boiler horsepower, but has also resultedin a reduction the feed pump pressure required toY force themed-Waterinto' the coil. For' example, previous. 50 horsepower units supplyingsteam; atA a pressure of 1100 lbs'` per square inch have required a feedpump pressure of 280 to 290 lbs. per square inch as compared with a feedwater pumppressure of 260 lbs.' per square inch for the-present unit;This indicates that less actual steam or vapor was formed in the heatingcoil 35v with'a greater'proportion of solid liquid than vapor, whichresulted in less friction flow loss through said coil. 11n practice,itis desired to maintain a streamef fluid flowing through the heatingcoil '35 containing a maximum ratio of V25% vapor to '75% liquid. Inother words, the reduction in the back pressure indicates that a greaterpercentage of heat is absorbed by the liquid and only a, comparativelysmall amount of the liquid is converted to vapor during the passage ofliquid through the heating coilbefore it discharges from the outlet pipe1I into a steam separator or other apparatus (not shown).

While the heating coil, combustion chamber lining means, and the meansfor maintaining a low jacket temperature have been described inconnection with a steam generating apparatus, it is to be understoodthat the invention is not limited to the use of these features inapparatus for generating steam, and that the invention contemplatestheir use wherever susceptible.

The details of the invention disclosed herein, other than the heatingcoil per se and the method of making the same, are -claimed in mycopending application Serial No. 688,721, filed of even date, as adivision hereof.

It will be understood that various changes may be made in the materialsand details of construction of the apparatus disclosed herein, and inthe method of making the heating coil, without departing from the spiritof the invention or the scope of the annexed claims.

I claim:

1. A heating coil, comprising: a preheater section having an inlet andan outlet and including a plurality of pancake coils connected inseries; a generating section having an inlet-and an outlet andcomprising spaced coils of pipe; and a water wall section comprising acontinuous coil having one end thereof connected with the outlet of thepreheater section and the other end thereof connected with the inlet ofsaid generating section, said preheater section being entirely abovesaid water wall section and said generating section being'substantiallycompletely within the upper portion of said water wall section.v

2. A heating coil, comprising: a preheater section having an inlet andan outlet and including a plurality of pancake coils connected inseries; a generating section having an inlet and an outlet and includinga plurality of pancake coils each' 3. A heating coil, comprising: apreheater section having an inlet and an outlet and includ- Ving aplurality of pancake coils connected in series; a generating sectionhaving an inlet and an outlet and including upper and lower pancakecoils with at least one pancake coil disposed therebetween and includingmeans interconvnecting the outlet of said upper pancake coil with theinlet of said lower pancake coil, and

means :connecting the outlet of 'said' lower pani cake coil with theinlet of saidintermediate pancake coil; and a water wall sectioncompris-A ing a continuous coil having one end thereof connected withthe outlet of said preheater section and the other end thereof connectedwith the inlet of lsaid upper pancake coil of said generating section.

4. A heating coil, comprising: a preheater section including a pluralityof coils Vconnected in series so that flow occurs downwardlyVVtherethrough; a water wall section comprising a continuous doubleWound coil having one end there# of connected with the outlet of saidpreheater section so that flow continues downwardly through one portionof said double wound coil and upwardly through another portion of saiddouble wound coil; and a generating section including vertically spacedcoils with theinlet of the upper coil of the generating sectionconnected with the other end of said water wall section and the outletthereof connected directly with the inlet of the lower coil of saidgenerating section so that flow again occurs downwardly, the outlet ofthe lower coil of said generating section being connected with the inletof the coil next adjacent thereto and the intermediate coils of thegenerating section being connected in series so that flow through theintermediate coils of said generating section occurs in an upwarddirection.

5. A heating coil, comprising: a preheater section including a pluralityof superposed pancake coils connected in series, the upper pancake coilhaving an inlet for the preheater section and the lower pancake sectionhaving an outlet for the preheater section; a water Wall sectiondisposed below said preheater section and including a continuous coilhaving one end thereof connected with the outlet of said preheatersection; and a generating section including a plurality of superimposedpancake coils disposed below said preheater section and within saidgenerating section, the inlet of the upper pan cake coil of saidgenerating section being connected with the other end of said water Wallsection and having the outlet thereof connected with the inlet of thelowermost pancake coil of said generating section, the outlet of saidlowermost pancake coil of said generating section being connected to theinlet of the next adjacent intermediate pancake section and saidintermediate pancake sections being interconnected in series so that thepancake coil adjacent the uppermost pancake coil of the generatingsection is provided with an outlet serving as a discharge for thecomplete coil assembly.

6. A heating coil, comprising, a cylindrical shell, a `preheater coil inthe upper portion of said shell, a water wall section below saidpreheater coil and including two interwound helical coils with theirends interconnected at the bottom by a return bend, said water Wallcoils being in continuous firm contact with the inside of said shell, agenerating coil having spaced apart tubes Within the upper portion ofsaid Water Wall section, the upper ends of the said helical coils beingconnected to the outlet of said preheater coil and the inlet of saidgenerating coil, respectively, the turns of said water wall sectionbeing axially spaced apart below said generator coil but in closecontact with each other throughout that part of the Water wall sectionextending around said generating coil.

7. A heating coil, comprising, a cylindrical l5 shell, awaterwallsection comprising a helically Wound coill in said shell with the turns.thereof infirm line contact with the inside of said shell, a generatingsection comprising a plurality of pancake. coils having spaced aparttubes, one above the other, arranged within and across the upper portionof said Water Wall section and defining a combustion chamber therebelow,the turns of said Water Wall section being in closeV contact with eachother throughout that portion of the Water Wall section` extendingaround said generating section but being Vertically spaced apart belowsaid generating section at the sides of said combustion chamber.

PERRY ARANT.

REFERENCES CITED Number Number 16 UNITED STA-TES- PAFI'ENTS- Name DateBaclizstrorn Feb. 27, 1917 Winslow Oct. 8, 1918 Quinnet' al Dec. 7, 1926Hall July 26, 1927 Billow O ct. 22, 1929 Elze June 24, 1930 Bottoms-June 27, 1933 Hamm etal Aug. 21, 1934 Baumann Aug. 20, 1935 SterrickyJuly 13, 1937 Bailey et al. Aug. 22, 1939 Goergi Jan. 9, 1940 McCulloughet al. Oct. 10, 1944 Livingood June 12, 1945 Arant May 9, 1950 FOREIGNPATENTS Country Date

